Rice agriculture is the foundation of Asian civilizations south of the Yangtze River. Although rice history is well documented for its lower Yangtze homeland area, the early southward expansion of ...paddy rice farming is poorly known. Our study investigates this process using a compilation of paleoenvironmental proxies from coastal sediment cores fromsoutheast China to Thailand and Island Southeast Asia.We propose that a shortage of land suitable for paddy fields, caused by marine transgression, constrained rice agriculture during the mid-Holocene. Rapid expansion of coastal plains, particularly in deltaic basins, over the past three millennia has coincided with increases in land suitable for rice cultivation. Our study also helps explain the past population movements of rice farmers.
In order to examine relative sea-level responses to the postglacial ice-volume change and the glacio-hydro isostatic adjustments (GIA), this study investigated the inner part of the Hangzhou Bay, ...east China, a tectonically relatively stable far-field location, and reconstructed the early to middle Holocene sea-level history. This investigation has established the elevational relationship between modern saltmarsh-mudflat and tidal levels based on diatom analysis for sea-level indicative meaning estimates, produced 17 high-quality sea-level index points, and simulated GIA processes for the study site. These results reveal that the relative sea level rose from −38.3 ± 1.6 m in c. 10,000 cal a BP to the present height by c. 7000 cal. a BP, and the average rate of sea-level rise decreased gradually from 19.6 ± 2.6 mm/a to 2.3 ± 1.5 mm/a during the 3000 years. This period of sea-level history was punctuated by two episodes of accelerated rise around 8200 and 7500 cal a BP. The relative sea level rose to 0.8 ± 1.4 m above msl by c. 6500 cal. a BP, followed by a gradual fall back to the present height at 4500 cal a BP, implying a different response to the potential additional ice melting between 7000 and 4000 cal a BP. A comparison of the sea-level histories between the inner and outer Hangzhou Bay indicates the coastal levering effect due to the marine inundation of the continental shelves. A further comparison between sea-level data from China and Malay Peninsula reveals different GIA effects between the Cathaysia-Yangtze Blocks and the Sundaland Block.
•A modern analogue between diatom zones and tide levels.•RSL rose from −38.3 ± 1.6 m in 10,000 cal a BP to present height by 7000 cal a BP.•Punctuated by two episodes of accelerated rise around 8200 and 7500 cal a BP.•Evidence of coastal levering during the early Holocene.•Different GIA responses of Cathaysia Block and Sundaland Block to IESL.
This study has collected and analyzed seven sediment cores from the Pearl River delta, from which 16 new and high-quality sea-level index points are generated using a new approach. This study has ...also re-checked and re-calibrated the previously published sea-level data from China's southeast coast with corrections made for tectonic subsidence and sediment compaction factors. These sea-level data indicate a rise of relative sea level from −49.3 ± 0.8 m to the present height between 10,500 and 7000 cal. a BP. This sea-level history is similar to those recorded from other far-field locations and ice-volume equivalent sea-level models. The early to early-middle Holocene sea-level history in the study area shows a phase of accelerated rise at a rate increasing rapidly from 16.4 ± 6.1 mm/a at 10,500 cal. a BP to 33.0 ± 7.1 mm/a at 9500 cal. a BP. This phase was followed by a period of rapid decrease in the rate of sea-level rise to 8.8 ± 1.9 mm/a at 8500 cal. a BP and 1.7 ± 1.3 mm/a at 7500 cal. a BP. During the past 7000 years, the relative sea level in the study area changed very little. This new and complete history of Holocene sea-level change supports the following findings: (1) no obvious higher-than-present sea-level highstand in the Holocene is found from the northern South China Sea; (2) certain proportion of the effects of the predicted glacial isostatic adjustment were cancelled out by the effects of the weak upper mantle viscosity in the study area; (3) meltwater pulse 1b likely exists spanning into the early Holocene; (4) there are significant misfit between sea-level data and glacial isostatic adjustment models, and a revision to the existing ice melting history for the early Holocene is possibly needed.
•New and high-quality sea-level index points of the early and early-middle Holocene are produced for the northern South China Sea.•The sea-level data are corrected for tectonic subsidence and sediment compaction factors.•The relative sea level rose from −49.3 ± 0.8 m to the present height from 10,500–7000 cal. a BP in an average rate of 13.7 ± 2.7 mm/a.•No obvious higher-than-present mid-Holocene sea-level highstand is observed in this region due to the weak upper mantle viscosity.•The rate of relative sea-level rise had varied and peaked at 33.0 ± 7.1 mm/a around 9500 cal. a BP.
Holocene sea-level rise, monsoonal discharge and human activity have been the main drivers for the evolutionary history of Asian deltas. In theory, when sea level ceased to rise in around 7000 cal. a ...BP, deltas should have started to prograde seawards. However, previous studies revealed that the progradation of modern deltas was initially very slow, and more importantly, sediment accumulation within central deltaic basins was exceptionally low between 7000 and 4000 cal. a BP. In order to investigate the main reasons for such slow progradation and low sedimentation during the middle Holocene, this study reconstructed the sedimentary history of the head area of the Pearl River delta. The results show marine transgression from 9500 to 7500 cal. a BP, followed by marine regression starting from 7500 to 4000 cal. a BP, in response to sea-level change. During the latter period, sedimentation was concentrated in the head area. The amount of sediment entering the central basin was significantly reduced. This limited amount of sediment was spread thinly across the wide deltaic basin. A portion of it could have been transported out into the South China Sea by the strong tidal currents, resulting in an exceptionally low sedimentation in the central basin. However, in locations adjacent to former/present islands, locally supplied sediment helped sedimentation to continue from 7500 to 4000 cal. a BP. By about 4000 cal. a BP, the deltaic shoreline advanced into the central basin. This period saw an increase of human activity that caused soil erosion and sediment supply, leading to a marked increase in sedimentation rate. Active land reclamations also helped the acceleration of shoreline advance. This sedimentary evolution model in the Pearl River delta mirrors those of other deltas in the monsoonal Asia.
•New sedimentary core records were reported for the head area of the PRD.•A three-stage history of the landform evolution in the head area was reconstructed.•Holocene sediment accumulation models were identified for the head area, central wide deltaic basin and peri-island area.•Reasons for the mid-Holocene low sedimentation in the PRD were discussed along with other Asian deltas.
The transition to the Late Holocene/Neoglacial occurred as a worldwide process of climatic deterioration from the optimum thermal conditions of the mid-Holocene, culminating in an abrupt decline ...around 4200 cal yr ago, in a period of severe climatic deterioration that lasted for two or three centuries. This sudden climatic event has been recorded in many proxy data archives from around the world, and its effects were manifest in different ways depending on the reaction of regional weather systems and conditions, but often as greatly increased aridity and/or cold temperatures. It has been regarded as causing or contributing to the sudden collapse of several well-established human societies at that time, including advanced agricultural Late Neolithic cultures in eastern China. We have used high-resolution pollen and non-pollen palynomorph analysis to examine the nature of this climatic transition through its impacts on the vegetation and hydrology at Pingwang, a site in the Yangtze coastal lowlands which has no evidence of complicating environmental influences such as sea-level rise or significant human land-use activity, factors previously suggested as alternative reasons for changes in forest composition. Our results show two phases of forest alteration, one gradual from about 5500 cal BP and one sudden at about 4200 cal BP., in which the frequencies of subtropical forest elements fall and are replaced by those of conifers and cold-tolerant trees. Total arboreal pollen frequencies do not decline and the proportion of temperate forest trees, tolerant of a wide range of temperatures, remains unchanged throughout, both ruling out human land clearance as a cause of the change in forest composition. As these dates accord very well with the known timings of climate deterioration established from other proxy archives in the region, we conclude that climate was the main driver of vegetation change in eastern China at the mid- to Late Holocene transition. Our hydrological results support the view that a combination of rising local water level and climatic cooling during the 4200 cal BP event was the probable cause of societal collapse in the lower Yangtze valley.
•We investigate the environmental transition to the Late Holocene at ca 4200 cal yr BP in east China.•Fine resolution pollen, non-pollen palynomorph and AMS radiocarbon analyses are used.•Two main phases of change in forest composition and local hydrology can be distinguished.•With no evidence of human activity nearby, these changes can be attributed to climatic deterioration.•Our results indicate that climate change and other natural factors led to late Neolithic cultural collapse.
The persistence and prevalence of microplastics in the environment have raised concerns among scientists, the general public, and environmental regulatory agencies, and a large number of studies on ...microplastics in sediments have been published. We reviewed those studies and focused on understanding the spatial and temporal variations, biological effects, and analytic methods of microplastics in sediments. Microplastics are widely distributed in marine and freshwater sediments. The distribution of microplastics is mainly influenced by anthropogenic input and environmental processes that determine the transportation, transformation and accumulation. The appearance of microplastics in sedimentary records has been proposed as a stratigraphic marker for the onset of the Anthropocene Epoch. Our current understanding of biological effects of microplastics is based mainly on field research and laboratory-scale experiments using unrealistic concentration and limited forms of microplastics. Future studies should consider environmentally relevant concentration, the diverse composition and form of microplastics presenting in the natural environment. Density separation method for separation of microplastics in sediments is the most commonly used, and component identification by optical analysis (Fourier-transform infrared spectroscopy spectra, Raman spectra etc.) are important analytic methods. Yet the separation method remains to be standardized across laboratories. Other separation methods include electrostatics separation, organic solvent extraction and magnet separation. We recommend the combination of density separation, electrostatic separation and organic solvent separation to improve the separation efficiency of microplastics and to standardize the analytic process for sediment microplastics in future studies.
In order to examine the role of human drivers in shoreline advance of the Pearl River delta plain over the past 7500 years, this study reconstructed several palaeo-shorelines based on sedimentary ...records, archaeological findings, historical archives, family ancestral books and modern survey data. With these shorelines, this study quantified the land growth rate for each of seven time periods spanning from the Neolithic-Bronze Ages, through the agricultural period, to the modern industrial era. The results show that, since c. 7500 cal. a BP as the sea level ceased to function as the primary driver, fluvial discharge and tide became the main natural drivers. Between 5500 BCE and 200 BCE, as fluvial discharge was progressively reduced, the amount of sediment drained out to the sea by tidal action was also progressively reduced due to the decrease of the estuarine space. As a result, the land growth rate was kept around 0.36–0.38 km2/a for this period. During the agricultural stage between 200 BCE and 1950 CE, human activity has led to a continuous increase of land growth rate, from 0.78 km2/a caused by land clearance (200 BCE to 960 CE) to 2.69 km2/a triggered by early land reclamation (960–1370 CE) and further to 4.50 km2/a as more advanced techniques were used (1370–1950 CE). Finally, a better organization of human power in land reclamation and the use of machinery since 1950 CE has accelerated the land growth to an average of 10.56 km2/a. The river damming and soil preservation projects in the past three decades have greatly reduced sediment supply and caused a significant slowdown in the shoreline advance.
•Sixteen deltaic shorelines of the past 7500 years were reconstructed.•Land growth rates of the delta plain were quantified.•The shoreline advance during 5500–200 BCE was dominated by natural drivers.•Human driver accelerated the delta advance during agricultural and industrial eras.•Levee construction and land reclamation played an important role in delta advance.
The peak period of marine isotope stage 5 (MIS5e) is the most recent warm period largely comparable to the present interglacial, marine isotope stage 1 (MIS1). The spatial variations in sea surface ...temperature (SST) between MIS5e and MIS1 can reveal the important differences in the effects of insolation and oceanographic conditions between the two warm periods, which in turns help refine global climate models. In order to quantify the differences, this study calculated the SST for the peak periods of MIS5e (c. 128-113 ka BP) and MIS1 (c. 8-3 ka BP) along the low-latitude western North Pacific margin (18 oN to 26 oN). Together with the previously published data from the South China Sea (9 oN to 19 oN), the results indicate a generally northwards decreasing trend in the two interglacial periods. This latitudinal SST trend in both peak MIS 1 and MIS 5e can be attributed to the strong influence of ocean currents in the studied region. Secondly, the average SST of peak MIS5e is 1.3 ± 0.2 °C higher than that of peak MIS1, suggesting a higher level of insolation during the previous interglacial. However, the above general pattern is complicated by the near-shore and offshore difference in the effects of winter monsoon on oceanic conditions around 20–22 oN. The coastal upwelling near 26 oN during peak MIS5e reduced the SST, whilst the SST was raised as the upwelling ceased during peak MIS1. Finally, the SSTs of the two warm periods are significantly higher than the present SST from 20 oN northwards, implying the influence of winter monsoon cold current in the Taiwan Strait.
•Northward SST decreasing trend might be controlled by ocean current.•ΔSST between peak MIS5e and MIS1 is 1.3 ± 0.2 °C.•Summer insolation may probably influence SST differences between periods.
This study presents a new model of Holocene ice-volume equivalent sea level (ESL), extending a previously published global ice sheet model (Bassett et al., 2005), which was unconstrained from 10 kyr ...BP to present. This new model was developed by comparing relative sea level (RSL) predictions from a glacial isostatic adjustment (GIA) model to a suite of Holocene sea level index points from China and Malay-Thailand. Three consistent data-model misfits were found using the Bassett et al. (2005) model: an over-prediction in the height of maximum sea level, the timing of this maximum, and the temporal variation of sea level from the time of the highstand to present.
The data-model misfits were examined for a large suite of ESL scenarios and a range of earth model parameters to determine an optimum model of Holocene ESL. This model is characterised by a slowdown in melting at ∼7 kyr BP, associated with the final deglaciation of the Laurentide Ice Sheet, followed by a continued rise in ESL until ∼1 kyr BP of ∼5.8 m associated with melting from the Antarctic Ice Sheet. It was not possible to identify an earth viscosity model that provided good fits for both regions; with the China data preferring viscosity values in the upper mantle of less than 1.5 × 1020 Pa s and the Malay-Thailand data preferring greater values. We suggest that this inference of a very weak upper mantle for the China data originates from the nearby subduction zone and Hainan Plume. The low viscosity values may also account for the lack of a well-defined highstand at the China sites.
•We present a new model of Holocene ice-volume equivalent sea-level (ESL) change.•First in depth modelling study of China and Malay-Thailand RSL data using a GIA model.•In the model ESL slows down at 7 kyr BP, due to the retreat of Laurentide Ice sheet.•A continued ESL rise of 5.8 m from 7 to 1 kyr BP is driven by melting from Antarctica.•China data is best fit with weak upper mantle due to impact of nearby subduction zone and Hainan Plume.
•Alkenone and GDGT biomarker records from the northern South China Sea coast.•Late Miocene-Pliocene Asian summer monsoon (ASM) evolution inferred.•Maximal ASM strength at 5.6-4.3 Ma corresponded to ...Pliocene warmer conditions.•Dominant ASM control shifted from temperature to Walker Circulation at ∼4.3 Ma.
The Pliocene climate, characterized by sustained global warmth and weakened Walker Circulation, might be a potential analogue of our future climate. How Asian Summer Monsoon (ASM) evolved over this period and its controlling mechanisms remain controversial, which limits our understanding of future monsoon behavior. Here, we present alkenone- and GDGT-based records reconstructed from the northern coast of the South China Sea, interpreted to document the strength of ASM-induced upwelling/mixing effect, to infer Late Miocene-Pliocene ASM variability. Cooler local sea surface temperatures occurred between ∼5.6 million years ago (Ma) and 4.3 Ma, corresponding to Pliocene warmer conditions, effectively capturing the cooling signal induced by summer upwelling. Our multiple biomarker records consistently indicate three phases of Late Miocene-Pliocene ASM evolution: weak ASM strength at ∼6.5–5.6 Ma, substantially enhanced strength at 5.6–4.3 Ma, and reduced strength but with a slightly strengthening trend after ∼4.3 Ma. The three features have been reported collectively from previous terrestrial and marine records. The close correspondence of the ASM strength to tropical temperature before ∼4.3 Ma suggests a dominant tropical temperature control, whereas the increasing ASM strength after that, opposite to temperature changes, implies that the developed Walker Circulation started to influence ASM strength over the Late Pliocene. Hence, tropical temperature and Walker Circulation appear to have exerted competing roles in the Late Miocene-Pliocene ASM evolution.
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